Waste materials from a number of sources contain mixtures of oils, grease, protein, fibers and water at varying percentages. Two examples are: grease trap materials and animal processing waste such as animal blood and animal meat originating from slaughterhouses.
Slaughterhouse wastes are a potential reservoir of bacterial, viral, prion and parasitic pathogens capable of infecting both animals and humans. Different methods for the disposal of such wastes currently exist, including composting, anaerobic digestion (AD), alkaline hydrolysis (AH), rendering, incineration and burning. However, these methods are expensive and fail for the most part in recovering the valuable byproducts in these wastes.
Grease trap material is a complicated solid/liquid mixture. Apart from small fibers, these materials contain water, food waste with protein-enriching components, including undigested protein, and oil with high Free Fatty Acids (FFA) content. An effective method of separating grease trap material may produce enriched nutrient clarified water, oil for animal feed, biodiesel feedstock and/or nutrient-rich organic solids for multiple uses.
The grease trap waste solids have a nitrogen content of around 3.51% that is a good source of protein. The nitrogen is in the form of indigestible forage proteins. Soluble protein in food waste hydrolyzes easily allowing the fermentation of sugars.
Some of the most expensive and reoccurring costs for water treatment facilities are the maintenance costs dealing with improper disposal of grease trap material. This occurs when restaurants fail to maintain the below ground grease traps or when grease haulers cannot find an appropriate place to offload the grease. The grease is then dumped into the municipal, county or private system or discarded onto open land. Both are not acceptable practices.
The materials originating from grease traps typically have a brown color from the frying they often undergo. Consequently, these materials are referred to as brown grease.
There are very few ways to manage this material without high-energy costs, expensive machinery, and a substantial odor issue. Examples of brown grease compositions are shown below in tables 1 and 2.
TABLE 1Brown Grease composition (All values are %).Brown Grease Composition(7 Samples Florida)Water content (% total)91Dry matter content (% total)6.5Crude protein (%)1.49Crude oil (%)3.51Crude fiber (%)0.235
TABLE 2Brown Grease elements content in seven samples.Brown Grease Solids CompositionElements(7 samples Florida)Phosphorus (% total)1.15%Potassium (% total)0.1%Sodium1.49%Kjeldahl Nitrogen3.51%Nitrogen3.51%Organic Carbon98%Nickel0.044%Zinc0.385%Cadmium0.00014%Chromium0.028%Copper0.0168%Molybdenum0.0001%
It would therefore be desirable to provide a process to separate these materials in order to maximize their uses.